PROJECT SUMMARY Epidemiological studies have consistently shown that chronic pain is a major factor contributing to insomnia. Chronic pain is typically treated with mu opioid receptor (MOP) agonists but the widespread misuse of prescription opioids has underscored the need to develop effective, non-addicting medications for pain. Agonists at the nociceptin/orphanin FQ (N/OFQ) receptor (NOPR) have shown considerable promise as modulators of the antinociceptive and rewarding effects of MOP agonists. Our preliminary studies with two different NOPR agonists demonstrate potent effects on non-Rapid Eye Movement (NREM) sleep and EEG delta power in rats and mice, suggesting that the N/OFQ-NOPR system may have a previously unrecognized role in sleep/wake regulation. Accordingly, we will begin to test the hypothesis that the N/OFQ-NOPR system is a component of the endogenous sleep/wake regulatory system. First, we will determine the basal sleep/wake characteristics and response to homeostatic sleep challenge in two strains of NOPR null mutant mice: a constitutive NOPR knockout and a conditional global NOPR knockout. If the N/OFQ-NOPR system is a component of the endogenous sleep/wake regulatory system, elimination of NOPRs would be expected to alter either the basal expression of sleep/wake or the homeostatic response to sleep deprivation. These studies will be complemented by intracerebroventricular injection of a NOPR agonist to demonstrate that the hypnotic effects are mediated centrally and are absent in NOPR knockout mice. We have also shown that N/OFQ terminals innervate hypocretin/orexin (Hcrt) neurons, that the N/OFQ peptide directly inhibits Hcrt neural activity in a dose-dependent manner, and that N/OFQ and corticotrophin releasing factor (CRF) coordinately regulate Hcrt cells in stress-induced analgesia (SIA). Given the critical role of the Hcrt system in maintaining wakefulness, we will test the hypothesis that the N/OFQ-induced increase in sleep is dependent upon an intact Hcrt system by assessing the efficacy of a NOP agonist on NREM sleep and EEG delta power in orexin/ataxin-3 mice, a strain in which the Hcrt neurons degenerate. This study will be complemented by one in which we will utilize the recently-described floxed NOPR mice to selectively eliminate NOPRs from the Hcrt neurons. Together, these experiments will provide an initial assessment of the hypothesis that the N/OFQ-NOPR system is a component of the endogenous sleep/wake regulatory system and will advance understanding of the neurobiology of the neuropeptidergic N/OFQ-NOPR system. 1